Journal articles: 'Optical atomic clocks'

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Ludlow, Andrew D., Martin M. Boyd, Jun Ye, E. Peik, and P. O. Schmidt. "Optical atomic clocks." Reviews of Modern Physics 87, no. 2 (June 26, 2015): 637–701. http://dx.doi.org/10.1103/revmodphys.87.637.

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Gellesch, Markus, Jonathan Jones, Richard Barron, Alok Singh, Qiushuo Sun, Kai Bongs, and Yeshpal Singh. "Transportable optical atomic clocks for use in out-of-the-lab environments." Advanced Optical Technologies 9, no. 5 (November 26, 2020): 313–25. http://dx.doi.org/10.1515/aot-2020-0023.

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AbstractRecently, several reports with a strong focus on compact, nonstationary optical atomic clocks have been published, including accounts of in-field deployment of these devices for demonstrations of chronometric levelling in different types of environments. We review recent progress in this research area, comprising compact and transportable neutral atom and single-ion optical atomic clocks. The identified transportable optical clocks strive for low volume, weight and power consumption while exceeding standard microwave atomic clocks in fractional frequency instability and systematic uncertainty. Some transportable clock projects additionally address requirements for metrology or serve the joint technology development between industrial and academic stakeholders. Based on the reviewed reports on nonstationary optical atomic clocks, we suggest definitions for transportable, portable and mobile optical atomic clocks. We conclude our article with an overview of possible future directions for developments of optical clock technology.

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Bondarescu, Ruxandra, Andreas Schärer, Andrew Lundgren, György Hetényi, Nicolas Houlié, Philippe Jetzer, and Mihai Bondarescu. "Ground-based optical atomic clocks as a tool to monitor vertical surface motion." Geophysical Journal International 202, no. 3 (July 16, 2015): 1770–74. http://dx.doi.org/10.1093/gji/ggv246.

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Abstract According to general relativity, a clock experiencing a shift in the gravitational potential ΔU will measure a frequency change given by Δf/f ≈ ΔU/c2. The best clocks are optical clocks. After about 7 hr of integration they reach stabilities of Δf/f ∼ 10−18 and can be used to detect changes in the gravitational potential that correspond to vertical displacements of the centimetre level. At this level of performance, ground-based atomic clock networks emerge as a tool that is complementary to existing technology for monitoring a wide range of geophysical processes by directly measuring changes in the gravitational potential. Vertical changes of the clock's position due to magmatic, post-seismic or tidal deformations can result in measurable variations in the clock tick rate. We illustrate the geopotential change arising due to an inflating magma chamber using the Mogi model and apply it to the Etna volcano. Its effect on an observer on the Earth's surface can be divided into two different terms: one purely due to uplift (free-air gradient) and one due to the redistribution of matter. Thus, with the centimetre-level precision of current clocks it is already possible to monitor volcanoes. The matter redistribution term is estimated to be 3 orders of magnitude smaller than the uplift term. Additionally, clocks can be compared over distances of thousands of kilometres over short periods of time, which improves our ability to monitor periodic effects with long wavelength like the solid Earth tide.

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Colombo, Simone, Edwin Pedrozo-Peñafiel, and Vladan Vuletić. "Entanglement-enhanced optical atomic clocks." Applied Physics Letters 121, no. 21 (November 21, 2022): 210502. http://dx.doi.org/10.1063/5.0121372.

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Recent developments in atomic physics have enabled the experimental generation of many-body entangled states to boost the performance of quantum sensors beyond the Standard Quantum Limit (SQL). This limit is imposed by the inherent projection noise of a quantum measurement. In this Perspective article, we describe the commonly used experimental methods to create many-body entangled states to operate quantum sensors beyond the SQL. In particular, we focus on the potential of applying quantum entanglement to state-of-the-art optical atomic clocks. In addition, we present recently developed time-reversal protocols that make use of complex states with high quantum Fisher information without requiring sub-SQL measurement resolution. We discuss the prospects for reaching near-Heisenberg limited quantum metrology based on such protocols.

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Nakamura, Takuma, Josue Davila-Rodriguez, Holly Leopardi, Jeff A. Sherman, Tara M. Fortier, Xiaojun Xie, Joe C. Campbell, et al. "Coherent optical clock down-conversion for microwave frequencies with 10−18 instability." Science 368, no. 6493 (May 21, 2020): 889–92. http://dx.doi.org/10.1126/science.abb2473.

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Optical atomic clocks are poised to redefine the Système International (SI) second, thanks to stability and accuracy more than 100 times better than the current microwave atomic clock standard. However, the best optical clocks have not seen their performance transferred to the electronic domain, where radar, navigation, communications, and fundamental research rely on less stable microwave sources. By comparing two independent optical-to-electronic signal generators, we demonstrate a 10-gigahertz microwave signal with phase that exactly tracks that of the optical clock phase from which it is derived, yielding an absolute fractional frequency instability of 1 × 10−18 in the electronic domain. Such faithful reproduction of the optical clock phase expands the opportunities for optical clocks both technologically and scientifically for time dissemination, navigation, and long-baseline interferometric imaging.

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Singh, Sukhjit, Jyoti, Bindiya Arora, B. K. Sahoo, and Yan-mei Yu. "Magic Wavelengths for Optical-Lattice Based Cs and Rb Active Clocks." Atoms 8, no. 4 (November 10, 2020): 79. http://dx.doi.org/10.3390/atoms8040079.

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Active clocks could provide better stabilities during initial stages of measurements over passive clocks, in which stabilities become saturated only after long-term measurements. This unique feature of an active clock has led to search for suitable candidates to construct such clocks. The other challenging task of an atomic clock is to reduce its possible systematics. A major part of the optical lattice atomic clocks based on neutral atoms are reduced by trapping atoms at the magic wavelengths of the optical lattice lasers. Keeping this in mind, we find the magic wavelengths between all possible hyperfine levels of the transitions in Rb and Cs atoms that were earlier considered to be suitable for making optical active clocks. To validate the results, we give the static dipole polarizabilities of Rb and Cs atoms using the electric dipole transition amplitudes that are used to evaluate the dynamic dipole polarizabilities and compare them with the available literature values.

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Ahmed, Mushtaq, Daniel V. Magalhães, Aida Bebeachibuli, Stella T. Müller, Renato F. Alves, Tiago A. Ortega, John Weiner, and Vanderlei S. Bagnato. "The Brazilian time and frequency atomic standards program." Anais da Academia Brasileira de Ciências 80, no. 2 (June 2008): 217–52. http://dx.doi.org/10.1590/s0001-37652008000200002.

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Cesium atomic beam clocks have been the workhorse for many demanding applications in science and technology for the past four decades. Tests of the fundamental laws of physics and the search for minute changes in fundamental constants, the synchronization of telecommunication networks, and realization of the satellite-based global positioning system would not be possible without atomic clocks. The adoption of optical cooling and trapping techniques, has produced a major advance in atomic clock precision. Cold-atom fountain and compact cold-atom clocks have also been developed. Measurement precision of a few parts in 10(15) has been demonstrated for a cold-atom fountain clock. We present here an overview of the time and frequency metrology program based on cesium atoms under development at USP São Carlos. This activity consists of construction and characterization of atomic-beam, and several variations of cold-atom clocks. We discuss the basic working principles, construction, evaluation, and important applications of atomic clocks in the Brazilian program.

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Lu Xiaotong, 卢晓同, and 常宏 Chang Hong. "光晶格原子钟研究进展." Acta Optica Sinica 42, no. 3 (2022): 0327004. http://dx.doi.org/10.3788/aos202242.0327004.

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HEO, Myoung-Sun, Dai-Hyuk YU, and Won-Kyu LEE. "High-Accuracy Optical Frequency Atomic Clock." Physics and High Technology 30, no. 3 (March 31, 2021): 2–7. http://dx.doi.org/10.3938/phit.30.005.

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Frequencies have been the most accurately measured physical quantity since the second was defined in 1967 based on the microwave atomic transition of a Cs atom. Recently, atomic clocks using optical frequency transitions have shown an order of magnitude better accuracy than microwave clocks. Thanks to their high accuracy and resolution, atomic clocks have become a new tool for investigations involving fundamental science and technology, such as the search for dark matter, gravitational wave detection, the temporal variation of fundamental constants, relativistic geodesy, quantum metrology, and the advanced Global Navigation Satellite System (GNSS). In addition, a redefinition of the second based on the optical frequency is expected. In this paper, we review the principles and applications of optical clocks.

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Delehaye, Marion, and Clément Lacroûte. "Single-ion, transportable optical atomic clocks." Journal of Modern Optics 65, no. 5-6 (March 7, 2018): 622–39. http://dx.doi.org/10.1080/09500340.2018.1441917.

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Wcisło, P., P. Ablewski, K. Beloy, S. Bilicki, M. Bober, R. Brown, R. Fasano, et al. "New bounds on dark matter coupling from a global network of optical atomic clocks." Science Advances 4, no. 12 (December 2018): eaau4869. http://dx.doi.org/10.1126/sciadv.aau4869.

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We report on the first Earth-scale quantum sensor network based on optical atomic clocks aimed at dark matter (DM) detection. Exploiting differences in the susceptibilities to the fine-structure constant of essential parts of an optical atomic clock, i.e., the cold atoms and the optical reference cavity, we can perform sensitive searches for DM signatures without the need for real-time comparisons of the clocks. We report a two orders of magnitude improvement in constraints on transient variations of the fine-structure constant, which considerably improves the detection limit for the standard model (SM)–DM coupling. We use Yb and Sr optical atomic clocks at four laboratories on three continents to search for both topological defect and massive scalar field candidates. No signal consistent with a DM coupling is identified, leading to considerably improved constraints on the DM-SM couplings.

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12

Zhang, Xibo, and Jun Ye. "Precision measurement and frequency metrology with ultracold atoms." National Science Review 3, no. 2 (March 15, 2016): 189–200. http://dx.doi.org/10.1093/nsr/nww013.

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Abstract Precision measurement and frequency metrology have pushed many scientific and technological frontiers in the field of atomic, molecular and optical physics. In this article, we provide a brief review on the recent development of optical atomic clocks, with an emphasis placed on the important inter-dependence between measurement precision and systematic effects. After presenting a general discussion on the motivation and techniques behind the development of optical lattice clocks, where the use of many atoms greatly enhances the measurement precision, we present the JILA strontium optical lattice clock as the leading system of frequency metrology with the lowest total uncertainty, and we describe other related research activities. We discuss key ingredients that have enabled the optical lattice clocks with ultracold atoms to reach the 18th digit in both precision and accuracy. Furthermore, we discuss extending the power of precision clock spectroscopy to study quantum many-body physics and to provide control for atomic quantum materials. In addition, we explore future research directions that have the potential to achieve even greater precision.

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13

Khabarova, Ksenia, Denis Kryuchkov, Alexander Borisenko, Ilia Zalivako, Ilya Semerikov, Mikhail Aksenov, Ivan Sherstov, Timur Abbasov, Anton Tausenev, and Nikolay Kolachevsky. "Toward a New Generation of Compact Transportable Yb+ Optical Clocks." Symmetry 14, no. 10 (October 20, 2022): 2213. http://dx.doi.org/10.3390/sym14102213.

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Optical atomic clocks are currently one of the most sensitive tools making it possible to precisely test the fundamental symmetry properties of spacetime and Einstein’s theory of relativity. At the same time, the extremely high stability and accuracy of compact transportable optical clocks open new perspectives in important fields, such as satellite navigation, relativistic geodesy, and the global time and frequency network. Our project aimed to develop a compact transportable optical clock based on a single ytterbium ion. We present the first prototype of the Yb+ clock (298 kg in 1 m3) and present several solutions aimed to improve the clock’s robustness to approach the demands of a space-qualified system. We present spectroscopic studies of a 435.5 nm quadrupole clock transition with Fourier-limited spectra of 25 Hz. The estimated instability of the output frequency at 1 GHz, which was down-converted with an optical frequency comb (OFC), is at the level of 9×10−15/τ, and the long-term instability and inaccuracy are at the level of 5×10−16. As the next steps, we present a new design for the clock laser and the OFC.

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Zhang, Xiaogang, Shengnan Zhang, Duo Pan, Peipei Chen, Xiaobo Xue, Wei Zhuang, and Jingbiao Chen. "Hanle Detection for Optical Clocks." Scientific World Journal 2015 (2015): 1–6. http://dx.doi.org/10.1155/2015/614737.

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Considering the strong inhomogeneous spatial polarization and intensity distribution of spontaneous decay fluorescence due to the Hanle effect, we propose and demonstrate a universe Hanle detection configuration of electron-shelving method for optical clocks. Experimental results from Ca atomic beam optical frequency standard with electron-shelving method show that a designed Hanle detection geometry with optimized magnetic field direction, detection laser beam propagation and polarization direction, and detector position can improve the fluorescence collection rate by more than one order of magnitude comparing with that of inefficient geometry. With the fixed 423 nm fluorescence, the improved 657 nm optical frequency standard signal intensity is presented. The potential application of the Hanle detection geometry designed for facilitating the fluorescence collection for optical lattice clock with a limited solid angle of the fluorescence collection has been discussed. The Hanle detection geometry is also effective for ion detection in ion optical clock and quantum information experiments. Besides, a cylinder fluorescence collection structure is designed to increase the solid angle of the fluorescence collection in Ca atomic beam optical frequency standard.

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15

Safronova, M. S., M. G. Kozlov, and C. W. Clark. "Blackbody radiation shifts in optical atomic clocks." IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control 59, no. 3 (March 2012): 439–47. http://dx.doi.org/10.1109/tuffc.2012.2213.

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Ma, Long-Sheng. "Optical Atomic Clocks-from Dream to Reality." Optics and Photonics News 18, no. 9 (September 1, 2007): 42. http://dx.doi.org/10.1364/opn.18.9.000042.

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Tarallo, Marco G. "Toward a quantum-enhanced strontium optical lattice clock at INRIM." EPJ Web of Conferences 230 (2020): 00011. http://dx.doi.org/10.1051/epjconf/202023000011.

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The new strontium atomic clock at INRIM seeks to establish a new frontier in quantum measurement by joining state-of-the-art optical lattice clocks and the quantized electromagnetic field provided by a cavity QED setup. The goal of our experiment is to apply advanced quantum techniques to state-of-the-art optical lattice clocks, demonstrating enhanced sensitivity while preserving long coherence times and the highest accuracy. In this paper we describe the current status of the experiment and the prospected sensitivity gain for the designed cavity QED setup.

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Piester, D., M. Rost, M. Fujieda, T. Feldmann, and A. Bauch. "Remote atomic clock synchronization via satellites and optical fibers." Advances in Radio Science 9 (July 29, 2011): 1–7. http://dx.doi.org/10.5194/ars-9-1-2011.

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Abstract. In the global network of institutions engaged with the realization of International Atomic Time (TAI), atomic clocks and time scales are compared by means of the Global Positioning System (GPS) and by employing telecommunication satellites for two-way satellite time and frequency transfer (TWSTFT). The frequencies of the state-of-the-art primary caesium fountain clocks can be compared at the level of 10−15 (relative, 1 day averaging) and time scales can be synchronized with an uncertainty of one nanosecond. Future improvements of worldwide clock comparisons will require also an improvement of the local signal distribution systems. For example, the future ACES (atomic clock ensemble in space) mission shall demonstrate remote time scale comparisons at the uncertainty level of 100 ps. To ensure that the ACES ground instrument will be synchronized to the local time scale at the Physikalisch-Technische Bundesanstalt (PTB) without a significant uncertainty contribution, we have developed a means for calibrated clock comparisons through optical fibers. An uncertainty below 40 ps over a distance of 2 km has been demonstrated on the campus of PTB. This technology is thus in general a promising candidate for synchronization of enhanced time transfer equipment with the local realizations of Coordinated Universal Time UTC. Based on these experiments we estimate the uncertainty level for calibrated time transfer through optical fibers over longer distances. These findings are compared with the current status and developments of satellite based time transfer systems, with a focus on the calibration techniques for operational systems.

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Hollberg, L., E. H. Cornell, and A. Abdelrahmann. "Optical atomic phase reference and timing." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, no. 2099 (June 26, 2017): 20160241. http://dx.doi.org/10.1098/rsta.2016.0241.

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Atomic clocks based on laser-cooled atoms have made tremendous advances in both accuracy and stability. However, advanced clocks have not found their way into widespread use because there has been little need for such high performance in real-world/commercial applications. The drive in the commercial world favours smaller, lower-power, more robust compact atomic clocks that function well in real-world non-laboratory environments. Although the high-performance atomic frequency references are useful to test Einstein's special relativity more precisely, there are not compelling scientific arguments to expect a breakdown in special relativity. On the other hand, the dynamics of gravity, evidenced by the recent spectacular results in experimental detection of gravity waves by the LIGO Scientific Collaboration, shows dramatically that there is new physics to be seen and understood in space–time science. Those systems require strain measurements at less than or equal to 10 −20 . As we discuss here, cold atom optical frequency references are still many orders of magnitude away from the frequency stability that should be achievable with narrow-linewidth quantum transitions and large numbers of very cold atoms, and they may be able to achieve levels of phase stability, Δ Φ / Φ total ≤ 10 −20 , that could make an important impact in gravity wave science. This article is part of the themed issue ‘Quantum technology for the 21st century’.

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Gill, Patrick. "When should we change the definition of the second?" Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 369, no. 1953 (October 28, 2011): 4109–30. http://dx.doi.org/10.1098/rsta.2011.0237.

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The microwave caesium (Cs) atomic clock has formed an enduring basis for the second in the International System of Units (SI) over the last few decades. The advent of laser cooling has underpinned the development of cold Cs fountain clocks, which now achieve frequency uncertainties of approximately 5×10 −16 . Since 2000, optical atomic clock research has quickened considerably, and now challenges Cs fountain clock performance. This has been suitably shown by recent results for the aluminium Al + quantum logic clock, where a fractional frequency inaccuracy below 10 −17 has been reported. A number of optical clock systems now achieve or exceed the performance of the Cs fountain primary standards used to realize the SI second, raising the issues of whether, how and when to redefine it. Optical clocks comprise frequency-stabilized lasers probing very weak absorptions either in a single cold ion confined in an electromagnetic trap or in an ensemble of cold atoms trapped within an optical lattice. In both cases, different species are under consideration as possible redefinition candidates. In this paper, I consider options for redefinition, contrast the performance of various trapped ion and optical lattice systems, and point to potential limiting environmental factors, such as magnetic, electric and light fields, collisions and gravity, together with the challenge of making remote comparisons of optical frequencies between standards laboratories worldwide.

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Lemke, Nathan D., Kyle W. Martin, River Beard, Benjamin K. Stuhl, Andrew J. Metcalf, and John D. Elgin. "Measurement of Optical Rubidium Clock Frequency Spanning 65 Days." Sensors 22, no. 5 (March 3, 2022): 1982. http://dx.doi.org/10.3390/s22051982.

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Optical clocks are emerging as next-generation timekeeping devices with technological and scientific use cases. Simplified atomic sources such as vapor cells may offer a straightforward path to field use, but suffer from long-term frequency drifts and environmental sensitivities. Here, we measure a laboratory optical clock based on warm rubidium atoms and find low levels of drift on the month-long timescale. We observe and quantify helium contamination inside the glass vapor cell by gradually removing the helium via a vacuum apparatus. We quantify a drift rate of 4×10−15/day, a 10 day Allan deviation less than 5×10−15, and an absolute frequency of the Rb-87 two-photon clock transition of 385,284,566,371,190(1970) Hz. These results support the premise that optical vapor cell clocks will be able to meet future technology needs in navigation and communications as sensors of time and frequency.

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Lewis, Ben, Rachel Elvin, Aidan S. Arnold, Erling Riis, and Paul F. Griffin. "A grating-chip atomic fountain." Applied Physics Letters 121, no. 16 (October 17, 2022): 164001. http://dx.doi.org/10.1063/5.0115382.

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Cold atom fountain clocks provide exceptional long term stability as they increase interrogation time at the expense of a larger size. We present a compact cold atom fountain using a grating magneto-optical trap to laser cool and launch the atoms in a simplified optical setup. The fountain is evaluated using coherent population trapping and demonstrates improved single-shot stability from the launch. Ramsey times up to 100 ms were measured with a corresponding fringe linewidth of 5 Hz. This technique could improve both short- and long-term stabilities of cold atom clocks while remaining compact for portable applications.

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Bravo, Tupac, Dennis Rätzel, and Ivette Fuentes. "Gravitational time dilation in extended quantum systems: The case of light clocks in Schwarzschild spacetime." AVS Quantum Science 5, no. 1 (March 2023): 014401. http://dx.doi.org/10.1116/5.0123228.

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The precision of optical atomic clocks is approaching a regime where they resolve gravitational time dilation on smaller scales than their own extensions. Hence, an accurate description of quantum clocks has to take their spatial extension into account. In this article, as a first step toward a fully relativistic description of extended quantum clocks, we investigate a quantized version of Einstein's light clock fixed at a constant distance from a large massive object like the Earth. The model consists of a quantum light field in a one-dimensional cavity in Schwarzschild spacetime, where the distance between the mirrors is fixed by a rigid rod. By comparing a vertical and a horizontal clock, we propose an operational way to define the clock time when the clock resolves gravitational time dilation on scales smaller than its extension. In particular, we show that the time measured by the vertical light clock is equivalent to the proper time defined at its center. We also derive fundamental bounds on the precision of these clocks for measurements of proper time and the Schwarzschild radius.

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Schiller, S., A. Görlitz, A. Nevsky, J. C. J. Koelemeij, A. Wicht, P. Gill, H. A. Klein, et al. "Optical Clocks in Space." Nuclear Physics B - Proceedings Supplements 166 (April 2007): 300–302. http://dx.doi.org/10.1016/j.nuclphysbps.2006.12.032.

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Ju, Bowen, Peter Yun, Qiang Hao, Shuai Nie, and Guobin Liu. "A low phase and amplitude noise microwave source for vapor cell atomic clocks." Review of Scientific Instruments 93, no. 10 (October 1, 2022): 104709. http://dx.doi.org/10.1063/5.0096589.

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A low-noise microwave source plays a key role in high-performance passive atomic clocks. Here, we propose and implement a microwave frequency synthesizer featuring a low phase and amplitude noise. With the help of a high-Q factor surface acoustic wave band-pass filter, we generate a microwave with targeted frequency by frequency multiplication of a low noise local oscillator at a radio frequency with the closest integer. At the frequency offset of 1 Hz, 10 Hz, 100 Hz, 1 kHz, and 10 kHz, the absolute phase noise of the output 3.417 GHz signal is −53.0, −83.3, −107.7, −119.2, and −124.0 dBc/Hz, respectively. After the microwave-to-optical conversion, the expected intermodulation effect contribution to the frequency stability of the coherent population trapping (CPT) atomic clock is 5.95 × 10−14 at an averaging time of 1 s. Meanwhile, with a feature of low fluctuation of this chain’s output microwave power at the level of 1.19 × 10−5 W at 1 s, its contribution to the frequency stability of the CPT atomic clock is 7.85 × 10−14 at the 1 s integration time. Our simple and low noise microwave chain is an ideal microwave source for high-performance, compact CPT clocks and could also be applied to cold atom or ion based microwave clocks.

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Takamoto, M., Y. Tanaka, and H. Katori. "A perspective on the future of transportable optical lattice clocks." Applied Physics Letters 120, no. 14 (April 4, 2022): 140502. http://dx.doi.org/10.1063/5.0087894.

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The unprecedented stability and accuracy of optical atomic clocks extend their role not only in frequency metrology but also in fundamental physics and geodesy. In particular, excellent stability of optical lattice clocks accessing a fractional uncertainty of [Formula: see text] in less than an hour opens a new avenue for chronometric leveling, which resolves a height difference of one cm in a short averaging time. However, for field use of such clocks, there remains a challenge in developing a transportable system that can operate outside the laboratory. In this Perspective, we describe transportable optical lattice clocks and discuss their future applications to chronometric leveling.

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Chen, Ding, Jiangning Xu, Yifeng Liang, Shan Jiang, and Hongyang He. "Long-Distance Time Transfer in Optical Fiber Networks Using a Cascaded Taming Technology." Mathematical Problems in Engineering 2021 (April 22, 2021): 1–10. http://dx.doi.org/10.1155/2021/8860028.

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In order to meet the time service needs of high-precision, long-distance, and multinode optical network, this paper proposes a new time synchronization solution, which combines the wavelength division multiplexing (WDM) technology with cascaded taming clock technology. The WDM technology is used for time synchronization between each pair of master-slave nodes. In the system, there are two wavelengths on the fiber link between the master node and the slave node for transmitting signals. 1 plus per second (PPS) signal, time code signal, and 10 MHz signal are, respectively, and successively, sent to the optical fiber link. By solving the one-way delay through analysis of error contribution and link characteristics of the time transmission process, time synchronization of the master-slave nodes pair is achieved. Furthermore, the authors adopt cascaded taming clock technology to ensure accurate time synchronization of each node. A 700 km long-distance time-frequency synchronization system is constructed in the laboratory. The system uses a cesium atomic clock as the reference clock source and transmits the signals through 8 small rubidium atomic clocks (RB clocks) hierarchically. Results from the experiment show that the long-term time stability is 47.5 ps/104 s. The system’s structural characteristics and the experiment results meet the requirements to allow practical use of high-precision time synchronization in networks. This proposed solution can be applied in various civil, commercial, and military fields.

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CACCIAPUOTI, LUIGI, and OLIVIER MINSTER. "FUNDAMENTAL PHYSICS ACTIVITIES IN THE HME DIRECTORATE OF THE EUROPEAN SPACE AGENCY." International Journal of Modern Physics D 16, no. 12a (December 2007): 1957–66. http://dx.doi.org/10.1142/s0218271807011255.

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The Human Spaceflight, Microgravity, and Exploration (HME) Directorate of the European Space Agency is strongly involved in fundamental physics research. One of the major activities in this field is represented by the ACES (Atomic Clock Ensemble in Space) mission. ACES will demonstrate the high performances of a new generation of atomic clocks in the microgravity environment of the International Space Station (ISS). Following ACES, a vigorous research program has been recently approved to develop a second generation of atomic quantum sensors for space applications: atomic clocks in the optical domain, aiming at fractional frequency stability and accuracy in the low 10-18 regime; inertial sensors based on matter-wave interferometry for the detection of tiny accelerations and rotations; a facility to study degenerate Bose gases in space. Tests of quantum physics on large distance scales represent another important issue addressed in the HME program. A quantum communication optical terminal has been proposed to perform a test of Bell's inequalities on pairs of entangled photons emitted by a source located on the ISS and detected by two ground stations. In this paper, present activities and future plans will be described and discussed.

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Abgrall, Michel, Baptiste Chupin, Luigi De Sarlo, Jocelyne Guéna, Philippe Laurent, Yann Le Coq, Rodolphe Le Targat, et al. "Atomic fountains and optical clocks at SYRTE: Status and perspectives." Comptes Rendus Physique 16, no. 5 (June 2015): 461–70. http://dx.doi.org/10.1016/j.crhy.2015.03.010.

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Radzewicz, Czesław, Marcin Bober, Piotr Morzyński, Agata Cygan, Daniel Lisak, Dobrosława Bartoszek-Bober, Piotr Masłowski, et al. "Accuracy budget of the88Sr optical atomic clocks at KL FAMO." Physica Scripta 91, no. 8 (July 14, 2016): 084003. http://dx.doi.org/10.1088/0031-8949/91/8/084003.

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Campbell, S. L., R. B. Hutson, G. E. Marti, A. Goban, N. Darkwah Oppong, R. L. McNally, L. Sonderhouse, et al. "A Fermi-degenerate three-dimensional optical lattice clock." Science 358, no. 6359 (October 5, 2017): 90–94. http://dx.doi.org/10.1126/science.aam5538.

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Strontium optical lattice clocks have the potential to simultaneously interrogate millions of atoms with a high spectroscopic quality factor of 4 × 1017. Previously, atomic interactions have forced a compromise between clock stability, which benefits from a large number of atoms, and accuracy, which suffers from density-dependent frequency shifts. Here we demonstrate a scalable solution that takes advantage of the high, correlated density of a degenerate Fermi gas in a three-dimensional (3D) optical lattice to guard against on-site interaction shifts. We show that contact interactions are resolved so that their contribution to clock shifts is orders of magnitude lower than in previous experiments. A synchronous clock comparison between two regions of the 3D lattice yields a measurement precision of 5 × 10–19 in 1 hour of averaging time.

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Horiuchi, Noriaki. "Ever-evolving optical lattice clocks." Nature Photonics 16, no. 1 (December 20, 2021): 4–5. http://dx.doi.org/10.1038/s41566-021-00935-3.

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Hänsch, T. W., J. Alnis, P. Fendel, M. Fischer, C. Gohle, M. Herrmann, R. Holzwarth, N. Kolachevsky, Th Udem, and M. Zimmermann. "Precision spectroscopy of hydrogen and femtosecond laser frequency combs." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 363, no. 1834 (August 2005): 2155–63. http://dx.doi.org/10.1098/rsta.2005.1639.

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Precision spectroscopy of the simple hydrogen atom has inspired dramatic advances in optical frequency metrology: femtosecond laser optical frequency comb synthesizers have revolutionized the precise measurement of optical frequencies, and they provide a reliable clock mechanism for optical atomic clocks. Precision spectroscopy of the hydrogen 1S–2S two-photon resonance has reached an accuracy of 1.4 parts in 10 14 , and considerable future improvements are envisioned. Such laboratory experiments are setting new limits for possible slow variations of the fine structure constant α and the magnetic moment of the caesium nucleus μ Cs in units of the Bohr magneton μ B .

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Cilluffo, Dario. "Statistical time-domain characterization of non-periodic optical clocks." Quantum 6 (July 14, 2022): 764. http://dx.doi.org/10.22331/q-2022-07-14-764.

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Measuring time means counting the occurrence of periodic phenomena. Over the past centuries a major effort was put to make stable and precise oscillators to be used as clock regulators. Here we consider a different class of clocks based on stochastic clicking processes. We provide a rigorous statistical framework to study the performances of such devices and apply our results to a single coherently driven two-level atom under photodetection as an extreme example of non-periodic clock. Quantum Jump MonteCarlo simulations and photon counting waiting time distribution will provide independent checks on the main results.

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Norcia, Matthew A., Matthew N. Winchester, Julia R. K. Cline, and James K. Thompson. "Superradiance on the millihertz linewidth strontium clock transition." Science Advances 2, no. 10 (October 2016): e1601231. http://dx.doi.org/10.1126/sciadv.1601231.

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Laser frequency noise contributes a significant limitation to today’s best atomic clocks. A proposed solution to this problem is to create a superradiant laser using an optical clock transition as its gain medium. This laser would act as an active atomic clock and would be highly immune to the fluctuations in reference cavity length that limit today’s best lasers. We demonstrate and characterize superradiant emission from the millihertz linewidth clock transition in an ensemble of laser-cooled 87Sr atoms trapped within a high-finesse optical cavity. We measure a collective enhancement of the emission rate into the cavity mode by a factor of more than 10,000 compared to independently radiating atoms. We also demonstrate a method for seeding superradiant emission and observe interference between two independent transitions lasing simultaneously. We use this interference to characterize the relative spectral properties of the two lasing subensembles.

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Mann, Adam. "Core Concept: Amazingly precise optical atomic clocks are more than timekeepers." Proceedings of the National Academy of Sciences 115, no. 29 (July 17, 2018): 7449–51. http://dx.doi.org/10.1073/pnas.1809852115.

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Riehle, Fritz. "Towards a redefinition of the second based on optical atomic clocks." Comptes Rendus Physique 16, no. 5 (June 2015): 506–15. http://dx.doi.org/10.1016/j.crhy.2015.03.012.

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DITTUS, HANSJÖRG, and CLAUS LÄMMERZAHL. "THE CLOCK MISSION OPTIS." International Journal of Modern Physics D 16, no. 12b (December 2007): 2499–510. http://dx.doi.org/10.1142/s0218271807011334.

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Clocks are an almost universal tool for exploring the fundamental structure of theories related to relativity. For future clock experiments, it is important for them to be performed in space. One mission which has the capability to perform and improve all relativity tests based on clocks by several orders of magnitude is OPTIS. These tests consist of (i) tests of the isotropy of light propagation (from which information about the matter sector which the optical resonators are made of can also be drawn), (ii) tests of the constancy of the speed of light, (iii) tests of the universality of the gravitational redshift by comparing clocks based on light propagation, like light clocks and various atomic clocks, (iv) time dilation based on the Doppler effect, (v) measuring the absolute gravitational redshift, (vi) measuring the perihelion advance of the satellite's orbit by using very precise tracking techniques, (vii) measuring the Lense–Thirring effect, and (viii) testing Newton's gravitational potential law on the scale of Earth-bound satellites. The corresponding tests are not only important for fundamental physics but also indispensable for practical purposes like navigation, Earth sciences, metrology, etc.

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Maurice, Vincent, Zachary L. Newman, Susannah Dickerson, Morgan Rivers, James Hsiao, Phillip Greene, Mark Mescher, John Kitching, Matthew T. Hummon, and Cort Johnson. "Miniaturized optical frequency reference for next-generation portable optical clocks." Optics Express 28, no. 17 (August 7, 2020): 24708. http://dx.doi.org/10.1364/oe.396296.

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Petit, G., D. N. Matsakis, D. C. Backer, G. Beutler, T. Fukushima, S. M. Leschiutta, E. Proverbio, et al. "Commission 31: Time: (L’heure)." Transactions of the International Astronomical Union 25, no. 1 (2002): 69–72. http://dx.doi.org/10.1017/s0251107x00001279.

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The relative frequency stability and the accuracy of atomic time scales, like International Atomic Time TAI, is now of order 1 × 10-15 thanks to progresses in clock technology and in clock comparison techniques. Cold atom primary Cs standards have a stated accuracy of 1 × 10-15 and a stability in the 10-16 region. Other cold atom clocks provide even better prospects, as well as clocks based on trapped ions. Frequencies based on optical and microwave transitions can now be compared with a similar or even better uncertainty thanks to femtosecond comb technology. Clock comparison techniques based on GPS (see http://maia.usno.navy.mil/gpst.html), or on dedicated Two Way technology provide adequate performance when averaging data over one or a few days, and should be improved to accompany the progresses of clocks.Since 1999, a number of organizations initiated a review on the future of the UTC system (insertion of leap seconds between TAI and UTC to keep |UT1 – UTC| < 0.9s). Several working groups have been initiated, notably by the International Telecommunications Union (Special Rapporteur Group (SRG) in the Working Party 7A), by the International Union of Radio Science, and by the IAU following Resolution B2(2000). No immediate conclusion may be foreseen but a consensus should be reached over the next triennium.

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Martin, M. J., M. Bishof, M. D. Swallows, X. Zhang, C. Benko, J. von-Stecher, A. V. Gorshkov, A. M. Rey, and Jun Ye. "A Quantum Many-Body Spin System in an Optical Lattice Clock." Science 341, no. 6146 (August 8, 2013): 632–36. http://dx.doi.org/10.1126/science.1236929.

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Strongly interacting quantum many-body systems arise in many areas of physics, but their complexity generally precludes exact solutions to their dynamics. We explored a strongly interacting two-level system formed by the clock states in 87Sr as a laboratory for the study of quantum many-body effects. Our collective spin measurements reveal signatures of the development of many-body correlations during the dynamical evolution. We derived a many-body Hamiltonian that describes the experimental observation of atomic spin coherence decay, density-dependent frequency shifts, severely distorted lineshapes, and correlated spin noise. These investigations open the door to further explorations of quantum many-body effects and entanglement through use of highly coherent and precisely controlled optical lattice clocks.

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McGrew, W. F., X. Zhang, H. Leopardi, R. J. Fasano, D. Nicolodi, K. Beloy, J. Yao, et al. "Towards the optical second: verifying optical clocks at the SI limit." Optica 6, no. 4 (April 11, 2019): 448. http://dx.doi.org/10.1364/optica.6.000448.

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Huang, M., D. K. Serkland, and J. Camparo. "A narrow-linewidth three-mirror VCSEL for atomic devices." Applied Physics Letters 121, no. 11 (September 12, 2022): 114002. http://dx.doi.org/10.1063/5.0101810.

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We consider the use of a recently invented three-mirror vertical-cavity surface-emitting laser (VCSEL) as an optical-pumping light source for next-generation atomic devices (e.g., atomic clocks). While VCSELs are attractive given their very low size, weight, and power and intrinsic resistance to longitudinal mode hops, their relatively large linewidths give rise to efficient laser phase-noise to transmitted intensity noise conversion (PM-to-AM), which severely limits the signal-to-noise ratio in vapor-cell signals. In contrast, the three-mirror VCSEL has a linewidth more than ten times narrower than traditional VCSELs. Using a three-mirror VCSEL in a continuous-wave Cs vapor-cell atomic clock testbed, we demonstrate the utility of this laser for next-generation atomic devices in general, obtaining a short-term stability of 3.6 × 10−12/ τ1/2 without any attention to PM-to-AM mitigation strategies.

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Chen, Sifei, Chang Liu, Shaohang Xu, Yuanhao Li, Jiale Wang, Yanhui Wang, Ying Liu, and Wenhai Jiao. "Beam optics analysis on magnetic-state-selected atomic clocks with optical detection." Journal of Applied Physics 131, no. 11 (March 21, 2022): 114401. http://dx.doi.org/10.1063/5.0083473.

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In traditional cesium beam clocks, cesium atoms are deflected by strong inhomogeneous magnetic fields. The distribution of the detectable atoms, which is critical to the short-term frequency stability, is hard to describe with analytical functions. In this paper, we numerically analyze the beam optics performance of cesium beam tubes based on the magnetic-state-selected and fluorescence detection scheme. To accurately model the cesium beam tube, we apply the Monte Carlo sampling directly inside the collimator. The finite element method is also applied to model the magnetic field. Upon the high dimensional distribution space, two key parameters are selected as indicators of the short-term performance of the cesium beam tube, the effective velocity distribution, and the normalized density difference of atoms in [Formula: see text] and [Formula: see text]. The influence of the configuration of the collimator is analyzed. Experiments are carried out with two manufactured beam tubes. The results show good agreement with the simulation model. We also discuss limitations of the simulation method when applied to designing cesium beam tubes.

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Kang, Songbai, Mohammadreza Gharavipour, Christoph Affolderbach, and Gaetano Mileti. "Stability limitations from optical detection in Ramsey‐type vapour‐cell atomic clocks." Electronics Letters 51, no. 22 (October 2015): 1767–69. http://dx.doi.org/10.1049/el.2015.1902.

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Najda, S. P., T. Slight, P. Perlin, O. Odedina, T. Suski, L. Marona, S. Stanczyk, et al. "Lateral grating DFB AlGaInN laser diodes for optical communications and atomic clocks." Journal of Physics: Conference Series 810 (February 2017): 012053. http://dx.doi.org/10.1088/1742-6596/810/1/012053.

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Jiang, Y. Y., A. D. Ludlow, N. D. Lemke, R. W. Fox, J. A. Sherman, L. S. Ma, and C. W. Oates. "Making optical atomic clocks more stable with 10−16-level laser stabilization." Nature Photonics 5, no. 3 (January 23, 2011): 158–61. http://dx.doi.org/10.1038/nphoton.2010.313.

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Pollock, J. W., V. I. Yudin, A. V. Taichenachev, M. Yu Basalaev, D. V. Kovalenko, A. Hansen, J. Kitching, and W. R. McGehee. "Inhomogeneous light shifts of coherent population trapping resonances." Applied Physics Letters 120, no. 15 (April 11, 2022): 154001. http://dx.doi.org/10.1063/5.0087391.

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Coherent population trapping (CPT) in atomic vapors using all-optical interrogation has enabled the miniaturization of microwave atomic clocks. Light shifts induced by the CPT driving fields can impact the spectral profile of CPT resonances and are a common limit to the long-term stability of CPT clocks. Nonlinear light shifts have been observed in several CPT systems and have not been explored in detail. In this Letter, we demonstrate that nonlinear light shifts in CPT clocks can arise from spatially inhomogeneous CPT driving fields. We measure this effect using Gaussian laser beams in a buffer gas cell and show strong agreement with a four-level model describing the CPT Λ-system with a noninteracting “trap” state. We estimate the effect of this nonlinearity on recently developed light shift mitigation techniques and suggest improvements to existing techniques.

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Horiuchi, Noriaki. "Publisher Correction: Ever-evolving optical lattice clocks." Nature Photonics 16, no. 2 (January 10, 2022): 170. http://dx.doi.org/10.1038/s41566-022-00954-8.

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Matsakis, Demetrios N., Frederick J. Josties, and Roger S. Foster. "Pulsar Astrometry and Improved Terrestrial Clocks." International Astronomical Union Colloquium 160 (1996): 113–14. http://dx.doi.org/10.1017/s025292110004118x.

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AbstractRecent improvements in cesium and hydrogen terrestrial frequency standards have brought the frequency precision of International Atomic Time (TAI) to a value of 2.5E-15 s/s over an averaging time of a month. In this paper we illustrate the improvement graphically, and discuss the state of the art for frame ties between the radio, dynamical, and optical frames. In a larger paper, available via the World Wide Web, we illustrate the measured accuracy curves of the frequency standards, show their effect on the ensemble time scales, explain the reasons for the confusing array of available time scales, and discuss the inverse problem of using pulsar data to correct the terrestrial time scale.

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Journal articles on the topic 'Optical atomic clocks'

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